Deborah Harkness’s novel “The Book of Life,” the third book in her planned trilogy about supernatural creatures, is topping bestseller lists.

“The Book of Life” was released on July 15 and debuted at number one for the Hardcover Fiction list on the Indiebound bestseller list for the week of July 24. “Book” also topped the bestseller list compiled by Reuters on July 25 and is at number one on the USA Today bestseller list for July 24.

Harkness’s trilogy centers on historian Diana Bishop, who is also a witch, and her love interest scientist Matthew Clairmont, who is a vampire, as they look for an old manuscript that may be able to tell the reader where supernatural creatures came from. The first book in the series, “A Discovery of Witches,” came out in 2011 and the second book, “Shadow of Night,” came out in 2012.

However, reviews so far have been mixed. NPR writer Genevieve Valentine found that “Harkness' style feels strained here, perhaps as a result of trying to scale a mountain of plot. Her love for alchemy and the details of spellcraft make Diana's witchy moments some of the book's most vibrant, standing out from the cavalcade of heavily populated subplots whose payoffs are rarely equal to the previous novels' escalating stakes.”

Washington Post critic Elizabeth Hand agreed, writing that “Where Harkness excels is with her charmingly offbeat details of witches and witchcraft… Harkness also does a deft job of weaving in details relating to alchemy, herb lore, and a few tongue-in-cheek references to Elizabethan historical figures… [but] newcomers to this saga would do best to start with the first volume, ‘A Discovery of Witches’… I’ve read both previous books and still found myself frantically trying to remember who was who.” She also said that “the plot is equally crowded… Harkness’s overly complicated plot scuppers some of the suspense in ‘The Book of Life,’ which suffers from the narrative fatigue that plagues so many massive, multi-volume supernatural family sagas. And can we please have a moratorium on vampire-non-vampire romances?”

Kirkus Reviews noted that there are “few surprises” but was otherwise more pleased with the book, writing that “there are healthy doses of action, colorful magic, angst-y romance and emotional epiphany, plus mansion-hopping across the globe, historical tidbits and name-dropping of famous artworks and manuscripts… it's still satisfying to travel with these characters toward their more-than-well-earned happy ending.”

And Library Journal writer Crystal Renfro of the Georgia Institute of Technology Library and Information Center found that “history, science, and the unpredictable actions of paranormal characters with hidden agendas all swirl together to create a not-to-be-missed finale to a stellar paranormal series,” though she also added that readers should really start with “Discovery.”